Trough line microstrip circulator with spaced ferrite surrounding transverse conductive rod



March 16, 1965 su TROUGH LINE MICROSTRIP CIRCULATQR WITH SPACED FERRITESURROUNDING TRANSVERSE CONDUCTIVE ROD Filed May 15, 1953 m R U0 m T newA hV Om I BIG Fig. 3. 37 39 United States Patent C TROUGH LINE MICRDSTRECIRCULATOR WITH SlACED FERRKTE SURRGUNDING TRANSVERSE CONDUCTIVE R01)John Sur, Honolulu, Hawaii, assignor to Hughes Aircraft Company, CulverCity, Calif., a corporation of Delaware Filed May 15, 1963, Ser. No.280,625 4 Claims. (Cl. 3333-11) This invention relates to a circulatorand more particularly to a trough line circulator capable of handlinghigh average power electromagnetic energy.

As is well known in the microwave component art, circulators arenonreciprocal junctions that have three or more ports and are usedextensively in radar duplexer, single cavity parametric amplifier, andswitching applications. The nonreciprocal property of these devices is afunction of a nonreciprocal element disposed symmetrically at thejunction. Generally, the nonreciprocal element comprises a ferrimagneticmaterial such as ferrite or garnet. The basic operational principles ofcirculators utilizing nonreciprocal elements will not be presented here,but may be found in various texts on the subject, such as MicrowaveFerrites and Ferrimagnetics by B. Lax and K. 3'. Button, McGraw-Hill,1962, pp. 517-539, 609-630.

The relatively large physical dimensions and weight of microwavecomponents has long been a problem sought to be overcome. A particularlycompact and light weight circulator has recently been constructed in theform of a strip-line junction and is described in detail in an articleentitled A Strip-Line L-Band Circulator in the Proceedings of theI.R.E., vol. 48, p. 115, 1960, by L. Davis, in, U. Milano, and J.Saunders.

Strip-line circulators have been utilized successfully throughout thevery high frequency to microwave frequency range with characteristicssuitable for most low and medium power radio frequency (RF)applications. However, where high RF power handling capability isrequired (over 500 watts average), the problem of heat is presented.

The input energy is transformed into heat in ferrimagnetic elements bythe presence of inherent losses in the ferrimagnetic material. The heatin turn affects the nonreciprocal magnetic properties of the elementuntil a term perature is reached where no circulator action takes place.This is known as the Curie temperature of the material. Furthermore,some ferrimagnetic materials exhibit an increase in losses astemperature is increased and thus leads to a runaway condition.

In the past, the only areas of the nonrecipcroal elements which had lowresistance heat conduction paths to an outer radiant surface in astrip-line circulator were the outer surfaces of the elements adjacentto the two ground planes. The areas of the elements adjacent the centerconductor junction, and the center conductor junction itself, had nosuch means to dissipate unwanted heat. Accordingly, these devices werelimited in the amount of power they could handle unless some externalmeans of carrying off the heat was utilized. The most successfulsolution to this problem has been to provide forced air cooling.However, this involves the use of heavy, bulky and expensive coolingsystems which defeat the principal advantages of compactness andlightness of weight which are derived from a strip-line type circulator.

From the above, it can be seen that a circulator which provides a lowheat resistance path to dissipate unwanted heat in the area of a centerconductor junction without degrading circulator performance would be asubstantial advance in the art.

It is therefore an object of the present invention to provide a compact,light weight circulator which will 0,,-

erate at high average power levels Without the necessity of forced aircooling.

This and other objectives are achieved according to this invention in atrough line circulator comprising at least three fiat strip centerconductors centrally disposed between, parallel to and spaced from apair of flat outer conductors. The three center conductors extend from acommon junction in a symmetrical relationship and in a common plane. Atransverse conductive rod is disposed at the center of the commonjunction and conductively connects the common junction with the flatouter conductors. Two nonreciprocal elements, each having a centrallylocated aperture, are disposed on opposite sides of the common junctionwith their apertures about the transverse rod. Also, a magnetic biasingfield means is magnetically coupled to the nonreciprocal elements forproviding therein a predetermined magnetic flux parallel to thetransverse rod.

Briefly, it may be stated that the transverse conductive rod inconjunction with an appropriate strip-line type of center conductorjunction can be thought of as transforming a strip-line circulator modeof operation into a waveguide circulator mode or, more specifically,what is commonly called a trough line mode of operation. In addition toproviding a low resistance thermo-conducting path from the centerconductor junction to the flat outer conductors or ground planes, theconductive rod may also provide mechanical support for the ground planeswhen four such circulators are used under common ground planes to reduceany undesirable eifects due to shock or vibration. A further advantagein the use of the transverse conductive rod is that the physicalsymmetry of the nonreciprocal elements can be accurately obtained.

The invention and specific embodiments thereof will be describedhereinafter by way of example and with reference to the accompanyingdrawing, in which:

FIG. 1 is a plan view of a preferred embodiment of a circulator providedin accordance with the present invention, the circulator having a topground plane partially removed;

Fit}. 2 is a cross-sectional view of the circulator of FIG. 1 takenalong the line 22;

FIG. 3 is a cross-sectional view of the circulator of FIG. 1 taken alongthe line 33; and

FIG. 4 is a plan view of a center conductor structure according toanother embodiment of the invention.

Referring now to the drawing and more particularly to FIGS. 1, 2 and 3,the present invention may be embodied in any desirable microwave systemor device incorporating coaxial or strip-line waveguiding means forpropagating electromagnetic energy. In the present instance, theinvention is embodied in a circulator 11 adapted to be interconnectedwith the abovementioned waveguiding means by a first connector 13, asecond connector 15 and a third connector 17.

Circulator 11 includes a first flat center conductor connected to thefirst connector 13, a second fiat center conductor 27 connected to thesecond connector 15 and a third fiat center conductor 2.9 connected tothe third connector 17. The three center conductors 25, 27, 29 are allsimilarly disposed between, parallel to and spaced from a pair of fiatouter conductors or ground planes such as a first common ground plane 31and a second common ground plane 33. These center conductors 25, 27, 29also extend from a common junction 35 in a symmetrical relationship andin a common plane to form a general strip-line circula-torconfiguration. Although any desired number of symmetrically positionedcenter conductors may be employed, the circulator 11, for illustrativepurposes, has three such conductors equally spaced apart) to form aso-called Y circulator.

A transverse conductive rod 37 which may be of brass or other conductivematerial is disposed at the center of the junction 35 and isconductively connected by any suitable means such as solder, forexample, to junction 35 as well as to both the first ground plane 31 andthe second ground plane 33. For ease of assembly, central-ly disposedholes 39, 41 have been provided in the two ground planes 31, 33,respectively, for accepting the conductive rod 37.

In order to provide circulator action in the circulator 11, a steadystate magnetic biasing field (from a source not shown) having adirection indicated by an arrow B is magnetically coupled to twononreciprocal elements such as a first ferrite element 43 and a secondferrite element 45, each of which has a centrally located aperture formounting about the transverse rod 3'7 in positions on opposite sides ofthe junction 35. The diameter of the ferrite elements 43, 45 are shownto be larger than the diameter of the common junction 35 merely forsimplicity and may have a different relationship depending upon thefrequency of the input energy to the circulator. As can be seen from thearrow B, the direction of the biasing field is parallel to thetransverse rod 37.

The strength of the biasing field to be used for circulator action will,as is well known, depend upon whether the device is to function in anabove or at below gyromagnetic resonance mode of operation. Theadvantages and disadvantages of operation in each of these modes and thebiasing field strength necessary to obtain them is discussed in theabove cited reference by B. Lax and K. J. Button.

The circulator 11 is enclosed by a cylindrical wall 47. It should benoted that the geometric configuration of the wall 47 will have littleeffect, if any, on the performance of the circulator 11. In fact, thecirculator 11 may be operated without the wall 47 with only a small lossof energy due to radiation. However, structure should then be providedto support connectors 12, 15 and 17.

It can readily be seen from FIGS. 2 and 3 that heat generated in the twoferrite elements 41, 45 has a very low resistance path to the outersurfaces of the two ground planes 31 and 33 provided by the transverserod 37.

As stated previously, the transverse rod 37 in effect transforms astrip-line circulator junction into a trough line circulator junction.The well known cross-sectional outline of a trough waveguide may be seenmost clearly in FIG. 3 by observing, for example, the section 31a of theground plane 31, section 35a of junction 35, seck tion 33a of groundplane 33, and the transverse rod 37.

For one practical embodiment of the invention as shown in FIGS. 13operating in the S-band frequency region (around 3 kmc.), the followingdimensions have been used:

Inches Inner diameter of the cylindrical wall 47 3.00 Width of the flatcenter conductors 25, 27, 29 0.425 Diameter of the common junction 351.075 Diameter of the conductive rod 37 0.125 Diameter of the ferriteelements 43, 45 1.075 Thickness of the ferrite elements 43, 45 H 0.130Length between the inner surfaces of ground planes For operation ofother frequencies, reference may be made to articles in the Transactionsof the IRE. on the subject of trough waveguides such as, for example,The Cut-Off Wavelength of Trough Waveguides by K. S. Packard in PGMTT,vol. 6, No. 4, pp. 455 and 456, October 1958, and Asymmetrical TroughWaveguide Antenna .by W. Rotman and A.A. Oliner in PGAP, vol. 7, No. 2,pp. 153-162, April 1959.

FIG. 4 illustrates a modification of the center condoctor structure ofFIG. 1. Here, parts corresponding to those of the arrangement of FIG. Ibear like reference characters. 'In the interest of simplicity, thecenter conductor structure is illustrated by itself. Its application inthe circulator will be evident from FIG. 1.

As shown, the center conductor structure is again generally of Y-shapedconfiguration having a flat circular center section 35. In this case,however, the periphery of the circular center section intermediate theconductors 25, 27 and 29 is notched or slotted radiaily as shown byreference character 40, providing a notch-type slow wave structure. Thisprovides a circulator requiring less ferrite material than the devicesshown in FIG. 1 because of the reduced wave propagation provided by theslow Wave structure.

As can be seen from the flat center conductor structure shown in FIGS. 1and 4, tapering may be utilized at the extremities of the centerconductors 25, 27, 29 coupled, by conventional means such as solder, tothe connectors 13, 15, 17 for impedance matching purposes.

From the foregoing, it will be evident that there is achieved a compact,light weight circulator capable of operating in high RF powerapplications.

Although only the 3-port Y configuration has been illustrated, it shouldbe appreciated that more than 3 ports may be provided, and otherorganizations of the specific arrangements shown may be made within thespirit and scope of the invention.

Accordingly, it is intended that the foregoing disclosure and theshowings made in the drawings shall be considered only as illustrationsof the principles of this invention and are not to be construed in alimiting sense.

What is claimed is:

1. A trough line circulator comprising: at least three flat strip centerconductors centrally disposed between, parallel to and spaced from apair of flat outer conductors, said center conductors extending from acommon junction in a symmetrical relationship in a common plane; atransverse conductive rod disposed at the center of said common junctionand conductively connecting said common junction with said pair of flatouter conductors; two nonreciprocal elements each having a centrallylocated aperture and disposed on opposite sides of said common junctionand with their apertures about said transverse rod; and magnetic biasingfield means magnetically coupled to said nonreciprocal elements forproviding therein a predetermined magnetic flux parallel to saidtransverse rod.

2. A trough line circulator comprising: at least three fiat strip centerconductors centrally disposed between, parallel to and spaced from apair of fiat outer condoctors, said center conductors extending from anessentially circular common junction in a symmetrical relationship in acommon plane; a transverse conductive rod disposed at the center of saidcommon junction and conductively connecting said common junction withthe flat outer conductors; two circular ferrite elements each having anaxial aperture and disposed on opposite sides of said common junctionand with their apertures about said transverse rod; and magnetic biasingfield means magnetically coupled to said ferrite elements for providingtherein a predetermined magnetic flux parallel to said transverse rod.

3. A trough line circulator comprising: at least three stripline flatstrip center conductors centrally disposed between, parallel to andspaced from a pair of flat outer conductors, said center conductorsextending from an essentially circular common junction in a symmetricalrelationship and in a common plane; a transverse conductive rod disposedat the center of said common junction and conductivcly connecting saidcommon junction with said pair. of outer conductors to form a troughline waveguiding structure at said common junction; two circular ferriteelements each having an axial aperture and disposed on opposite sides ofsaid common conductor junction and with their apertures about saidtransverse dm gnetic biasing field means magnetically. Coupied to saidferrite elements for providing therein a predetermined magnetic fluxparallel to said transverse rod.

4. A trough line circulator comprising: at least three fiat strip centerconductors centrally disposed between, parallel to and spaced from apair of flat outer conductors, said center conductors extending from anessentially circular common junction in a symmetrical relationship andin a common plane; a transverse bnass rod disposed at the center of saidcommon junction and conductiveiy connecting said circular commonjunction with said flat cuter conductors to form a trough lineWaveguiding structure at said common junction, said circular commonjunction being radially notched on its outer periphery intermediate saidcenter conductors to provide a slow Wave trough line structure at saidcommon junction; two circular ferrite elements each having an axialaperture and disposed on opposite sides of said common junction and withtheir apertures about said transverse rod; and magnetic biasing fieldmeans magnetically coupled to said ferrite elements for providingtherein a predetermined magnetic flux magnitude parallel to saidtransverse rod.

References tilted by the Examiner UNITED STATES PATENTS OTHER REFERENCESChait et al.: Electronics, Dec. 18, 1959, New Micro- Wave Circulators,pages 81-83 relied upon.

Milano et al.: Y-Junction Circulator, IRE Transactions on MicrowaveTheory and Techniques, May 1960, pages 345-350 relied upon.

Auld: Synthesis of Circulators, IRE Transactions on Microwave Theory andTechniques, April 1959, pages 238-246 relied upon.

Bland: Ferrite Y Circulator, IBM Technical Disclosure Bulletin, vol. 4,No. 10, March 1962, pages 45 and 46.

HERMAN KARL SAALBACH, Primary Examiner.

0 ELI LIEBERMAN, Examiner.

1. A TROUGH LINE CIRCULATOR COMPRISING: AT LEAST THREE FLAP STRIP CENTERCONDUCTORS CENTRALLY DISPOSED BETWEEN, PARALLEL TO AND SPACED FROM APAIR OF FLAT OUTER CONDUCTORS, SAID CENTER CONDUCTORS EXTENDING FROM ACOMMON JUNCTION IN A SYMMETRICAL RELATIONSHIP IN A COMMON PLANE; ATRANSVERSE CONDUCTIVE ROD DISPOSED AT THE CENTER OF SAID COMMON JUNCTIONAND CONDUCTIVELY CONNECTING SAID COMMON JUNCTION WITH SAID PAIR OF FLATOUTER CONDUCTORS; TWO NONRECIPROCAL ELEMENTS EACH HAVING A CENTRALLYLOCATED APERTURE AND DISPOSED ON OPPOSITE SIDES OF SAID COMMON JUNCTIONAND WITH THEIR APERTURES ABOUT SAID TRANSVERSE ROD; AND MAGNETIC BIASINGFIELD MEANS MAGNETICALLY COUPLED TO SAID NONRECIPROCAL ELEMENTS FORPROVIDING THEREIN A PREDETERMINED MAGNETIC FLUX PARALLEL TO SAIDTRANSVERSE ROD.